Modern military radar systems face increasingly difficult operational demands. Surveillance may require constant scanning of a hemisphere for targets having small radar cross-sections and which move at high speed, such as incoming cruise missiles. Simultaneous with this surveillance, the radar may be required to individually track identified targets, which may number in the tens or even in the hundreds. The power transmission and processing capability are strained by the combination of such requirements.
New and emerging threats further complicate the problem of providing radar resources. One of the more serious recent threat capabilities which tends to limit radar resources is that of hostile or “threat” targets which maneuver with accelerations of several times the force of gravity (g's). Such maneuvering targets can cause a radar system to lose track or fail to update the position of the target. If the target is hostile, the loss of track can compromise the ability to take successful countermeasures, such as engagement of the target with an interceptor missile. FIG. 1 illustrates in an overall fashion a scenario in which the maintenance of track is important, as described in U.S. Pat. No. 7,663,528, to Malakian et al., entitled Missile Boost-Ballistic Estimator now U.S. Pat. No. 7,663,528. In FIG. 1, a system 10 includes a radar 12 with an antenna illustrated as 12a, which may be an array antenna. Radar 12 generates electromagnetic signals which are transmitted by antenna 12a, as suggested by “lightning bolt” symbol 14. Radar 12 can operate in both a volume surveillance and target tracking mode. If there is a target within range of the radar 12, a portion of the transmitted signals will be reflected back toward the radar. In this case, a hostile target illustrated as a missile 16 is present. Missile 16 may be in powered (boost) flight, or it may be in unpowered (ballistic) flight. In any case, target 16 causes reflected or return signals return along the same path illustrated as 14 to the radar system. The radar system 12 processes the reflected signals to produce information relating to at least target slant range, and possibly bearing and elevation. These are referred to as “kinematic” features of the target. Target velocity and acceleration are determined by examining the position as a function of time, and acceleration is determined as the rate of change of velocity. The kinematic features, velocity and acceleration appear at an output port 12o of radar 12, and are coupled to an interceptor missile fire control system 94. Fire control system 94 estimates the actual current location of the target missile 16, and also estimates its trajectory or path 16p. Fire control system 94 generates fire control solutions, initiates the interceptor missile 322 while it is still at the interceptor launcher 92. Fire control system 94 commands a launch of the interceptor missile, and also tracks the location of the interceptor missile 322. Fire control system 94 guides the interceptor 322 toward the expected intercept point 88 after launch.
In its volume surveillance mode, radar 12 of FIG. 1 must provide information relating to all the targets within its surveillance volume. This surveillance volume may include many targets, including friendly targets, neutral targets, hostile targets, and targets of unknown nature. Modern radar systems generally use array antennas, well known in the art. Volume surveillance is accomplished with array antennas by generating separate beams in sequence. These separate beams are generated in sequence, and the beamwidths are selected to overlap, so that over a full volume scan all targets in the volume are illuminated with at least some energy. The rapidity of the generation of the pencil beams during volume scanning depends, at least in part, on the time required for the transmitted electromagnetic energy to travel to the target and for the reflection from the target to return to the radar. Such volume scanning requires generation of many “pencil” beams as quickly as the energy travel time allows. Ideally, the pencil beams have narrow beamwidth, in order to aid in particularly identifying the azimuth and elevation angle at which each target appears. However, the use of pencil beams that are very narrow undesirably increases the time required for a complete volume scan. The use of narrow beams is desirable in the tracking mode, however. Thus, there is a tension between the beamwidth requirements for optimal tracking and optimal volume surveillance.
Ideally, each mode of operation of a multimode volume search and tracking radar would use a number of pulses per unit time optimized for the range and size of the target to be searched for or tracked. Thus, more pulses per unit time can be used to increase the number of reflected signals from the target and to thereby improve the signal-to-noise ratio, but this adversely affects the amount of radar resources required for other functions, such as search or tracking, and also adversely affects the number of target objects that the radar can handle.
Alternative or improved radar systems are desired.